1. Technical Field
The present invention relates to a signaling transmitting/receiving circuit of a data multiplexer used in an Integrated Services Digital Network (i.e., ISDN), and more particularly to a signaling transmitting/receiving circuit of a primary multiplexer (i.e., PMUX).
2. Background Art
An ISDN is a communication system in which a single data channel can be used concurrently for multiple communications. The ISDN is a digital switching network or system which provides end-to-end signal connectivity and uses an out-of-band signaling capability. The end-to-end digital connectivity allows signals to enter the network in digital form, transport and then deliver to the subscriber in said digital form. This feature of the ISDN can eliminate the need for a modem which converts the digital signals into analog form for transmission over an analog telephone network. The out-of-band signaling feature allows the signaling information required to administer various communication functions, such as call setup, call monitoring, call waiting tones etc. . . . to be transmitted to the central office switch by a separate signaling channel. This feature of the ISDN can eliminate the need to use channel space in a talk path for administrative purposes. In an ISDN switching network, all signals, whether voice, data, or administrative, are transferred in digital form. There are two types of ISDN communication channels are provided to the subscriber, known as B-channel (i.e., two 64 Kbps channels) and D-channel (i.e., one 16 Kbps channel). B-channel contains voice or data information; and D-channel contains signaling and/or data information. Both the B and D channels are multiplexed to form a single ISDN serial data stream containing subscriber information (voice and data) and subscriber control (signaling) for transmission over a common communication channel. Both B and D channels are bi-directional.
To achieve multiple communications, a narrow band ISDN switching system has a unit accommodating basic access subscribers with primary access subscribers; the unit of accommodating basic access subscribers with primary access subscribers is known as a primary multiplexer (i.e., PMUX). The PMUX multiplexes basic access subscribers as many as the number of primary access links in order to connect the number of basic access subscribers to the ISDN switching system.
The ISDN switching system connected to the PMUX comprises an interface called a BAMI BLOCK. The BAMI BLOCK simply means a constitution of an ISDN switching system connected to a PMUX. A CV-channel is a channel for transmitting/receiving data between the PMUX and the BAMI BLOCK, and signaling data (i.e., CV-channel data) is data transmitted and received through the CV-channel for supporting management functions required for the ISDN switching system. Thus, the interface between the PMUX and the BAMI BLOCK should always maintain the reliability of CV-channel data transmission for inter-communication.
If the ISDN communication service starts, the number of basic access subscribers at remote positions from the ISDN switching system will increase. Accordingly, in order to provide good service for remote subscribers, errorless transmission of CV-channel data having information on layer 1 is required. To assure that the CV-channel data is signaling data transmitted between the PMUX and the BAMI BLOCK as described above, primary digital repeater of a T1 or a E1 type is used to ensure the fidelity of information transmitted between the PMUX and the BAMI BLOCK.
A PMUX can serve several subscribers through a single transmission line. In using that single transmission line, a frame arrangement for .respective time slots is provided, and a serial data stream transmitted/received through a PCM-highway.
Conventional signaling channel data transmitting/receiving circuits of a primary multiplexer having the constitution of the BAMI BLOCK within the ISDN switching system have been employed in order to insert the CV-channel data into the CV-channel, or to extract the CV-channel data from the CV-channel. It has been my observation that these conventional circuits are not only extremely complicated to construct, but also require extra hardware for the insertion and extraction of CV-channel data into/from the CV-channel. Moreover, I have noticed that during the extraction of the CV-channel data from the CV-channel, serial data stream continuously received with a short period is scanned, thereby creating a problem of large overhead associated with a program.